The present invention relates to an erasable image forming material.
With the recent progress of office automation, the amounts of various pieces of information are significantly increasing, and information output by hard copies is increasing accordingly. Hard copy output is the most basic image display means and superior in versatility and storage stability. However, hard copy output uses large amounts of paper as a recording medium when the information amount increases, and this leads to an increase use of wood resources as the material of paper. Forest resources are very important to maintain the terrestrial environment and suppress the greenhouse effect caused by carbon dioxide. Therefore, it is an important subject to minimize the use of wood resources and efficiently use the paper resources that we presently possess.
Conventionally, paper resources are recycled by processing paper sheets, on which image forming materials are printed, by using large amounts of a bleaching agent and water and remaking paper fibers to manufacture recycled paper with low paper quality. This method raises the cost of recycled paper and causes new environmental pollution resulting from waste liquor disposal.
Hence, the present inventors are developing an image forming material that contains a leuco dye, a developer, and a decolorizer compatible with these components, can form images in the same manner as common image forming materials, and allows formed images to be erased by processing the material with heat or a solvent. Use of this erasable image forming material makes it possible to repeatedly reuse paper sheets any number of times by returning the paper sheets to blank paper sheets by erasing images, with minimum degradation of paper quality. Since recycle need only be done when the paper quality significantly degrades by the reuse, the use efficiency of paper resources greatly improves. In this manner, the essential paper use amount can be reduced, so deforestation can be minimized. Additionally, it is possible to minimize any increase in cost of recycled paper and the environmental pollution by waste liquor disposal that are problems in the present recycle system.
Since this erasable image forming material is a novel material, conditions which can raise the image density in color formation and can well erase images are unclear.
More specifically, common toner or ink uses a completely colored dye, so the image density can be substantially determined by the content of a dye in the toner or ink. In contrast, an erasable image forming material forms color by the interaction between a color former and a developer in the presence of a decolorizer, so factors that determine the image density are very complicated.
Also, when an erasable image forming material is used as toner for electrophotography, if the amounts of a color former and a developer are increased to raise the image density, the amount of a decolorizer also needs to be increased accordingly. When the mixing amounts are thus changed, the ratio of a binder resin reduces compared with common toner. As a consequence, offset (a phenomenon in which toner sticks to a heat roller) readily occurs in the toner fixing process. Analogously, if the ratio of a vehicle (resin or wax) of printing ink reduces, the viscosity or the lipophilic nature degrades. This may pose various problems in the printing process.
On the other hand, the erase characteristics of an erasable image forming material have not been taken into consideration in the past. Accordingly, conditions by which a good erased state can be obtained are naturally unknown.